STEP 3 of 3:
(a) First EXIT your Flightradar24 feeder, or dump1090, or RTL1090 or ModeSdeco2 or any other software which is using DVB-T to make the Dongle free for test.
(b) Un-zip RelWithDebInfo.zip. It will create a folder RelWithDebInfo.
Inside this folder there is another folder rtl-sdr-release which contains several files and 2 folders named x32 and x64.
(c) Go to folder x32. You will find many rtl tools in it as shown in screenshot-1.
(d) Double-click file rtl_test.exe to run it.
A command console will open and if Dongle is OK, it will give output as shown in screenshot -2.

SCREENSHOT-1

SCREENSHOT-2

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OPTION-2: Dongle plugged into Raspberry Pi.

STEP-1:
Install the test tools package rtl-sdr

Code:

sudo apt-get update
sudo apt-get install rtl-sdr

NOTE: If you have a PI24 image, the above commands sometimes fail to install rtl-sdr due to "read-only file system".
In this case, issue following command to make the system "read and write", and after this, again run above commands to install rtl-sdr.

Code:

sudo mount -o remount ,rw /

STEP-2:
Stop dump1090 to free your Dongle for test

Code:

#choose one of the following commands,
#depending on which version of dump1090 you have installed.
#If you are not sure, issue all three one by one (some of these commands will say "not found")
sudo systemctl stop fr24feed
sudo systemctl stop dump1090
sudo systemctl stop dump1090-fa
sudo systemctl stop dump1090-mutability

STEP-3:
Now run the test command

Code:

rtl_test -t

If your Dongle is OK,
AND
Properly connected to Pi,
you will see this output

In tutorial below it will be changed from default 00000001 to 00000000. This may help solving Windows 10 problem

(A) Dongle Plugged into Raspberry Pi

STEP-1
First stop the dump1090 to make Dongle free for use by rtl tools.

Code:

#Give one of the command according to version of dump1090 you have installed
#If you are not sure of version, give all three commands one by one
sudo systemctl stop dump1090
sudo systemctl stop dump1090-mutability
sudo systemctl stop dump1090-fa

STEP-2
Install package rtl-sdr, if not yet done.
The tool rtl_eeprom is part of package rtl-sdr

Code:

sudo apt-get update
sudo apt-get install rtl-sdr

STEP-3
Now give the command rtl_eeprom -s 00000000 to reset the serial number
The last line of output will ask confirmation to go ahead with change.
Type y and press Enter key

STEP-3
Save the file as change-serial.bat
While saving, make sure that
1. File name contains .bat at the end
2. "Save as type" is selected "All Files" Please see screenshot below.

STEP-4
Double click the file change-serial.bat to run it

STEP-5
Upon double clicking the file change-serial.bat, command console will open, with last line asking confirmation to change serial number.
Type y and press Enter key. The serial number will change and command console will close immediately.

STEP-6
To check if the number has actually changed, again double click the file change-serial.bat, and it will show changed serial number.
Type n and press Enter key to close console

Using RTL1090 on Windows

Step-1: Open Command Promt, and give command C:\rtl1090>rtl1090.exe /eeprom
(My rtl1090.exe is located in folder C:\rtl1090, that is why I have used this path. You have to use the path in your computer)

This error comes when rtl_test command is given while dump1090 is running.
You have to STOP dump1090 by issuing one of following commands according to version of dump1090 you have
(if you are not sure of version of dump1090, issue all the three commands)

Following are possibilities
(1) The Dongle is not properly plugged into Pi. Unplug and replug it, and reboot Pi.
(2) If dongle is connected to Pi through a USB Cable, the cable is defective
(3) AC to 5V DC Power adapter is not good.
(4) Dongle is defective.

Thanks - I did try a repost earlier but doesnt seem to have been approved (or declined) by mods.

I have changed PSU and also used the "All to Easy" install, I have found that upon boot it will work for about 30 seconds then stops working not tracking - at this point even if I execute sudo systemctl stop dump1090-mutability and then the rtl_test -t I will get the error about not being able to lock the device, if I physically unplug the USB DVBT stick and replug then the rtl_test -t will give this result:

weirdness: rtlsdr gave us a block with an unusual size (got 0 bytes, expected 262144 bytes)
Sun Apr 22 18:08:35 2018 BST No data received from the dongle for a long time, it may have wedged

I am using a Rpi Model B, I have changed to a different 2.1a 5v PSU with the same issue and tried a different fresh SD card, I purchased my DVBT off ebay and the seller is kindly shipping another for me to try in case it is faulty.

Second dvb stick had the same issues so I tested on windows 10 which worked fine, I am thinking the raspberry pi model b isn’t giving enough power so will try a powered usb hub if not I’ll need to invest in a newer pi